Carswell studied medicine at Glasgow and Aberdeen, receiving his M.D. from Aberdeen in 1826. In 1828 he was made Professor of Morbid Anatomy at University College, London. Later he was appointed physician to the King of the Belgians, and was knighted by Queen Victoria for his services to Louis-Philippe during his exile in Britain. At the beginning of his career Carswell had spent five years in Paris and Lyon, where he made over two thousand watercolour drawings of diseased tissues, a selection of which were published in his Pathological anatomy, originally issued in twelve fascicles between January 1833 and January 1838. The atlas, one of the finest pathological atlases ever produced, is notable for the fine artwork of its forty-eight plates, drawn on stone by Carswell from his own watercolours, lithographed by A. Ducot? and Day & Haghe, and finished with hand colouring.